An internal memo of the carrier mentions the update will be available later today

Everyone is expecting for Microsoft to start the rollout of the Windows Phone 7.8 update, as promised. Even though the Redmond-based company said it would release the major upgrade for older Windows Phone handsets, it did not mention any exact release dates.

According to the latest hearsay, Windows Phone 7.8 should arrive for the newest devices on January 30, while the much older smartphones are expected to receive the update in February/March.

For the time being, there are is no telling which specific device will get the update and which one will be receive it.

However, we can safely assume that all Nokia Lumia phones, along with the newest smartphones made by other brands will get the update at some point in the next few weeks.

One of the first Windows Phone 7.5 handsets slated for a major upgrade is Nokia Lumia 900. We reported last week AT&T plans to offer customers who purchased the smartphone through its official channels the chance to be among the first to update their devices to Windows Phone 7.8.

As WPCentral reported less than a week ago, the carrier is ready to kick off the deployment of the update for Lumia 900 on January 30.

Today, the folks over at Engadget got another confirmation that the US-based carrier is indeed preparing for the Windows Phone 7.8 rollout.

An internal memo from AT&T mentions Microsoft software update 7.8 for Nokia Lumia 900 (SW version 2175.2307.8858.12480) is scheduled for later today.

The new software will only be available via Zune desktop software, so Lumia 900 users will need to connect their phone to their computers in order to go through the update process.

Windows Phone 7.8 is said to bring lots of new improvements, including a new start screen, new theme colors, better lock screen accidental wipe protection, Marketplace enhancements and more. Stay tuned for more info on the matter.